Project Summary Noise-induced hearing loss (NIHL) has reached epidemic levels in the USA, affecting an estimated 24.4% of adults and up to 17% of youths age 12-19. However, there are currently no treatments to prevent or reverse NIHL, in part because we know remarkably little about how noise damages the inner ear. We hypothesize that understanding the cellular and molecular mechanism by which noise damages the inner ear will help in creating new medicines for NIHL. The effects of noise are usually very rapid, e.g., many are evident immediately after a damaging exposure, suggesting they are mediated by changes in metabolism, which can occur rapidly, as opposed to resulting from effects on gene expression, which can take hours to manifest. Very little is known about the impact of noise on the inner ear metabolome. We believe that defining the effects of noise on the inner ear metabolome will fill a critical gap in knowledge, i.e., how noise damages the inner ear, and could lead to the identification of targets for future therapies. In preliminary proof-of-concept studies, we found that liquid chromatography/mass spectroscopy (LC/MS)-based metabolomics profiling is a powerful approach for the accurate characterization of inner ear metabolites and how these are affected by noise. We used targeted metabolomics on freshly harvested inner ears to define the relative abundance of 220 metabolites, which includes coverage of the major pathways in central carbon metabolism. We found that noise exposure induces acute changes in the inner ear metabolome and that these effects have high statistical significance and consistency. We also found that the impact of noise on the inner ear metabolome depends on the intensity and duration of exposure. Pathway analysis of the altered metabolites suggests that noise exposure activates redox and glutamate pathways. We now propose to develop this methodology further and to explore the effects of noise on the inner ear in an untargeted approach by working on two specific aims. In Aim 1 we will determine the impact of noise on the inner ear by performing untargeted metabolomics and lipidomics in mice with different types of noise exposures. In Aim 2 we will determine the contribution of hair cells and their activity to the noise- induced metabolic changes by testing the effects of noise on the inner ear metabolome and lipidome of mice lacking hair cells or capacity for mechano-transduction.